Conventionally, as a printed wiring board on which electronic components are to be packaged, a printed wiring board obtained by laminating a plurality of prepregs including a glass-epoxy resin and members including copper foil on each other, integrating and hardening thereof has been used. With miniaturization and improvement of performance of devices, electronic components such as semiconductors are required to be densely packaged. Thus, there is a demand for thinning of an insulating layer according to miniaturization and for high connection reliability of a through hole or a via hole suitable for high-density wiring.
One example of a problem about delamination is described. Since delamination may cause swelling during reflow, a method of subjecting wiring used for an inner layer to chemical treatment or physical polishing so as to increase the surface roughness, thereby enhancing adhesion between the wiring on the inner layer and the insulating layer is carried out.
In order to form highly precise wiring and, at the same time, to enhance copper foil peel strength, a method for increasing the roughness of a resin surface by dissolving the resin with, for example, an alkaline solution before an electroless plating process, followed by forming a plated conductor, thus enhancing the anchoring effect is employed.
Furthermore, in order to enhance the connection reliability, the following method is carried out. A through hole is processed by using a drill, and then desmear treatment prior to electroless plating is carried out to dissolve resin of an insulating layer portion on the inner wall surface of the through hole, thereby enhancing the surface roughness. After that, by enhancing adhesion of electrolytic copper produced on the inner wall surface of the through hole by electroless plating and electrolytic plating processes to the wall surface of the through hole, the anchoring effect between the wall surface of the through hole and the electrolytic copper is enhanced, and the connection reliability in, for example, a thermal-shock test is enhanced.
In a conventional printed wiring board, however, as wiring is being made to be finer so that it corresponds to high-density wiring, it is necessary to improve adhesion between the wiring and the insulating layer and between a resist and the insulating layer for fine patterning. Furthermore, the amount of resin is being reduced because of thinning of the insulating layer according to the miniaturization, and as a result, delamination occurs due to shortage of the adhesion force of the inner layer.
Furthermore, steps of soft etching treatment may be complicated. In order to enhance the adhesion between a wiring pattern and an insulating layer, for example, PTL 1 proposes a method of providing excellent adhesion to a wiring board without carrying out soft etching treatment. However, this method may be insufficient to correspond to fine patterning. Furthermore, when a plated conductor is thinned for forming a fine pattern and the density of the wiring is further increased, during heating or in heat cycle conditions, in through holes and via holes, disconnection caused by cracks due to a difference in the thermal expansion coefficients between these members, peeling with respect to the insulating layer and the plated conductor, and the like, occur. As a result, sufficient connection reliability cannot be secured.